Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

Show paginator

Hide paginator

25%

Page 1 of 4

1. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

2. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

4.33

3.33

1.33

3. The freezing point of sulphur dioxide is

-56.6°C

-75.2°C

-135.8°C

-77.7°C

4. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

5. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

5.12

6. A bootstrap air cooling system has

One heat exchanger

Four heat exchangers

Two heat exchangers

Three heat exchangers

7. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Centrifugal

Piston type reciprocating

8. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

1: 1

1: 9

9: 1

9. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Same

Less

10. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will evaporate

A gas will never liquefy

Water will never evaporate

Page 2 of 4

11. Which of the following statement is correct?

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

12. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Rankine

Reversed Carnot

Carnot

13. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

None of the above

Ensures the evaporator completely filled with refrigerant of the load

14. The capillary tube, as an expansion device, is used in

Domestic refrigerators

All of these

Water coolers

Room air conditioners

15. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Brine

Carbon dioxide

Freon

16. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Compressor and condenser

Evaporator and compressor

Receiver and evaporator

17. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Takes place at constant pressure

Involves no change in volume

Takes place at constant temperature

18. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Wet vapour

Saturated liquid

Dry saturated vapour

19. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

20. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

Super-cooling

None of these

Normal cooling

Page 3 of 4

21. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Always less than unity

Always more than unity

Equal to unity

22. Cooling water is required for following equipment in ammonia absorption plant

Absorber

Evaporator

Condenser, absorber and separator (rectifier)

Condenser

23. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Dry bulb temperature of air

Wet bulb temperature of air

Ambient air temperature

24. Most thermostatic expansion valves are set for a superheat of

20°C

5°C

15°C

10°C

25. The operating pressure for refrigerating units using R-12 as a refrigerant is

2 bar

15 bar

30 bar

8 bar

26. The boiling point of ammonia is

-10.5°C

-33.3°C

-77.7°C

-30°C

27. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.6

0.376

0.67

28. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

29. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

30. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Above critical temperature

Much below critical temperature

Near critical temperature of refrigerant

Page 4 of 4

31. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Condenser tubes

Capillary tubes

Evaporator tubes

32. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Detect liquid in vapour

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

33. Freon group of refrigerants are

Inflammable

Toxic

Non-inflammable and toxic

Nontoxic and non-inflammable

34. The curved lines on a psychrometric chart indicates

Relative humidity

Wet bulb temperature

Dew point temperature

Dry bulb temperature

35. Rating of a domestic refrigerator is of the order of

10 tons

0.1 ton

40 tons

5 tons

36. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Good electrical conductor

Low boiling point

Large latent heat

37. For obtaining high COP, the pressure range of compressor should be

High

Optimum

Low

Any value

38. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

39. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Negative

Positive

Zero

40. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Stirling

Ericson

Carnot

Share this Now with Friends:

VideRime

A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

Related

Leave a ReplyCancel reply

Ads by Google

Recent Posts

Membership Registration

Secured Payment

Protection